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Plant Physiology 74:645-649 (1984)
© 1984 American Society of Plant Biologists

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Articles

Propylamine Transferases in Chinese Cabbage Leaves 1

Ram K. Sindhu and Seymour S. Cohen

Department of Pharmacological Sciences, State University of New York at Stony Brook, Stony Brook, New York 11794

We have found spermidine synthase and spermine synthase activities in extracts of leaves of Chinese cabbage (Brassica pekinensis var. Pak Choy) and have developed an assay of the former in crude extracts. The method is based on the transfer of the propylamine moiety of decarboxylated S-adenosylmethionine to labeled putrescine, followed by ion-exchange separation of the labeled amine substrate and product, which are then converted to the 5-dimethylamino-1-napthalene sulfonyl (dansyl) derivatives and further purified and identified by thin layer chromatography. The specific radioactivity of putrescine present in the reaction mixture is determined, as is the radioactivity present in dansyl spermidine. The enzyme is also present in extracts of spinach leaves.

Spermidine synthase has been purified about 160-fold from Chinese cabbage leaves. After partial purification, a rapid coupled enzymic assay has been used to study various properties of the enzyme. The plant enzyme shows maximum activity at pH 8.8 in glycine-NaOH buffer and has a molecular weight of 81,000. The Km values for decarboxylated S-adenosylmethionine and putrescine are 6.7 and 32 micromolar, respectively. The enzyme activity is inhibited strongly by dicyclohexylamine, cyclohexylamine, and S-adenosyl-3-thio-1, 8-diaminoctane. Of these, dicyclohexylamine is the most potent inhibitor with an I50 at 0.24 micromolar.

1 Supported by grants from the National Science Foundation (PCM 78-0434) and the National Institutes of Health (1RO1 GM25522).






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Copyright © 1984 by the American Society of Plant Biologists